Pasture matrix promotes the increase of generalist ant species in forest fragments

Tropical forests have a high level of habitat loss, suffering an intensive process of forest fragmentation. The increasing pressure of farming and cattle ranching is one of the main causes of this problem, influencing the animal community by the environmental homogenization. To understand the impact of this homogenization on the native community structure that occurs in fragmented landscapes, we analyzed a set of environmental variables. A set of hypothesis were formulated to evaluate which factors can be employed to make pastures matrix more permeable to ant’s biodiversity and to understand how the ant’s communities are structured in pasture systems. To sample the ants, pitfall traps were used with a saturated saline solution and detergent. The traps were placed in transects inside the fragments in direction to matrix’s interior. We utilized three forest fragments and three matrices of pastures. Ten traps were placed in each of these and the following environmental variables were measured: richness and density of plants, diameter at breast height – DBH and quantity of leaf litter. The study was carried out between March and April of 2011. The ant communities were evaluated in distinct scales (punctual and fragment/matrix) to better represent the effect of a set of environmental variables, or some variables isolated, on these communities. We collected 89 species of ants, most of them classified as generalists. We identified 54 species (24 genera) and 57 spp. (25 genera) in forest fragments and pasture matrices, respectively . We found 28.1% of species (18.75% of genera) exclusively in the forest fragments; while 31.5% of spp., (25% of genera) was exclusively found on pastures. There was no significant relationship between environmental variables and ant richness (p>0.05). There was a difference between the compositions of functional groups, where more generalist species were found in pastures matrix. These results reveal that ants use the available local resources, but the composition of microhabitats make the distinction of species in functional groups. The pressure that generalist species can perform on the other functional groups can lead to great consequences, such as local extinction. We conclude that the pasture can be a facilitator of the generalist species entrance in forest fragments surrounded by it, which can be changing the local richness.